Quick answer
“Gemini Pro” and “GPT-5” can refer to different versions. This comparison is specifically about Gemini 2.5 Pro (gemini-2.5-pro) and GPT-5.5 (gpt-5.5). The documented API features differ, but they don’t establish which model will perform better on your workload.
There is an unresolved discrepancy between Google’s documentation: the Gemini API model reference says access is restricted to users who have actively used the 2.5 models and that they “will continue to be served until further notice,” while the Google AI Studio model page says Gemini 2.5 Pro is deprecated and that API requests will route to Gemini 3.8 Flash starting December 1, 2026. Both notices concern API access, but the pages do not explain the difference. As of November 12, 2026, check the notice that applies to your account and API channel before relying on this model. (aistudio.google.com)
For inputs involving audio, video, or PDFs, Gemini 2.5 Pro lists those modalities; GPT-5.5 lists text and image input, but not audio or video. GPT-5.5 lists a maximum output of 128,000 tokens, compared with Gemini 2.5 Pro’s 65,536. These are documented specifications, not evidence of comparative answer quality. (aistudio.google.com)
Production API comparison
| Consideration | Gemini 2.5 Pro | GPT-5.5 |
|---|---|---|
| API model ID | gemini-2.5-pro |
gpt-5.5; snapshot gpt-5.5-2026-04-23 |
| Access notice | The Gemini API model reference limits access to existing users who actively used 2.5 models. The AI Studio model page says the model is deprecated and API requests will route to gemini-3.8-flash on Dec. 1, 2026. Google’s pages do not reconcile these statements. |
Listed in OpenAI’s API model documentation. |
| Input and output | Text, image, audio, video, and PDF input; text output | Text and image input; text output. Audio and video are not supported. |
| Token limits | 1,048,576 input tokens; 65,536 output tokens | 1,050,000-token context window; 128,000 maximum output tokens |
| Listed API capabilities | Function calling, structured outputs, code execution, file search, search grounding, URL context, caching, and Batch API are listed as supported. | Streaming, function calling, and structured outputs are supported. Web search, file search, code interpreter, and other listed tools are supported when using the Responses API. |
Sources: Google Gemini API model reference, Google AI Studio model page, and OpenAI GPT-5.5 model page. (aistudio.google.com)
Practical fit: consider Gemini 2.5 Pro if its listed input modalities or capabilities fit your application and your account can access it. Account for Google’s December 1 routing notice in migration planning. Consider GPT-5.5 for text-and-image tasks that fit its limits, particularly if you plan to use its documented Responses API tools. Neither choice is a general quality winner; compare them on representative tasks.
API pricing: one side remains unverified
OpenAI lists GPT-5.5 standard rates at $5 per 1 million input tokens and $30 per 1 million output tokens. For prompts with more than 272,000 input tokens, its documentation says standard, batch, and flex sessions are charged at 2× the input rate and 1.5× the output rate for the full session. OpenAI also says reasoning tokens count toward output usage and are billed as output tokens. (developers.openai.com)
I could not verify a current, model-specific Gemini 2.5 Pro rate in the retrieved official Google pricing material, so this is not a complete price comparison. Google’s pricing page distinguishes free, paid, and enterprise tiers, but the retrieved text did not provide Gemini 2.5 Pro’s rates. Check the current price for your Google API billing channel before budgeting. (aistudio.google.com)
GPT-5.5 example: suppose a set of standard synchronous requests totals 1 million input tokens and 200,000 billable output tokens, including any reasoning tokens. If each individual prompt stays at or below 272,000 input tokens, and there are no cache discounts or other charges, the estimate is $5 + (0.2 × $30) = $11. This is an arithmetic example, not a monthly forecast. (developers.openai.com)
How to choose for your workload
- Confirm model IDs and access. For Gemini 2.5 Pro, check the availability notice applicable to your account and API channel; Google’s pages differ on whether and how long access continues.
- Test representative tasks on both APIs. Keep prompts, inputs, output requirements, and tool access as comparable as possible. Record model IDs and settings.
- Score quality against predefined criteria. Depending on your use case, assess correctness, required fields, grounded answers, output format, or whether generated code passes your tests.
- Measure operational results. Track latency, failures, retries, input and output tokens, and tool charges. Apply each provider’s current rates to your actual usage.
- Plan for a Gemini migration if needed. Google’s AI Studio notice names Gemini 3.8 Flash as the routing destination from December 1, 2026. Test that model separately rather than assuming identical behavior or cost. (
ai.google.dev)
Bottom line: Gemini 2.5 Pro lists broader input modalities, while GPT-5.5 has a documented output limit of 128,000 tokens and published API rates. Google’s pages give different Gemini 2.5 Pro availability statements, and its current price could not be verified here. Confirm access and billing, then use a paired pilot to decide for your workload.
Sources
Gemini 2.5 Pro | Gemini API | Google AI for Developers
Gemini 2.5 Pro | Gemini API | Google AI Studio
Gemini deprecations | Gemini API | Google AI Studio
Gemini Developer API pricing | Gemini API | Google AI Studio